About two months ago we added altitude hold using the Maxbotix sonar to the ArduCopter (you can find instructions re how to set it up on the wiki). At the moment on the we recommend the LV-EZ4 and XL-EZ4 but that's not based on a lot of research or experience so the question to the community is:
Which one of the Maxbotix sonars is best for our purpose?
Above you can some pics extracted from the datasheets of the four sensors. Each is a 1 foot grid and shows the theoretical range within which the sonar can sense a 3.5 inch pole (look at the black lines, not the red dots)
The first choice is whether the extra cost of the XL over the LV is worth it - according to the data sheet the XL's range is 80% better (nearly twice the range) which makes me think "yes".
The next choice (for either LV or XL lines) is between the EZ0 (fat-beam but longer range) or EZ4 (narrow-beam but shorter range). We went with the EZ4 because we thought the narrow beam would make the altitude correction using roll/pitch work better but I guess we might be able to correct for the fat-beam of the EZ0 in the code and then we'd benefit from the longer range..but perhaps we would also get more false readings?
So my guess is it should be the XL-EZ0 or LV-EZ0 but it would be great if people especially those who have played with sonars could voice their opinion/experience. Also at least one person has had trouble with the XL-EZ4 over carpets and grass so if people have experience over various surfaces we'd love to hear about it!